I like to go ahead and heat my brine to help dissolve the salt and leech out some of the flavors of any spices or herbs that I am using so they will absorb better, the only draw back is that I have to wait until the brine cools down enough not to cook the meat. (I sometimes add ice to cool the brine). I have also tried using bags to contain the brine, but have pretty much gone to a couple of Rubbermaid type plastic containers that work pretty well for most stuff. I think that the greater the volume of the brine, the better the process works. But for like a marinade that cost a little more than just salt and water, I will use a bag or even the vacpac that the meat originally came in.
You should follow and learn from a few recipes about the strenth of the brines and the times in the brine for different meats and cuts and keep track of what you like best for what. You can brine to the point of just adding a little flavor or to the point of everything coming out about like a good ole country ham.